Production of coated malleable iron castings



Jan, w, 1933. L. H. MARSHALL PRODUCTION OF COATED MALLEABLE IRONCASTINGS Filed Jan. 2. 1930 I I I I I LHW A TTOE/VE'K Patented Jan. 10,1933 UNIED LESLIE H. MARSHALL, OF COLUMBUS, OHIO, ASSIGNOR TO THETECHNIMET COMPANY, OF COLUMBUS, OHIO, A CORPORATION OF OHIO PRODUCTIONOF COATED MALLEABLE IRON CASTINGS Application filed January 2, 1930.Serial No. 417,978.

-' sitated a separate process of manufacture and this, of course, makesthe castings produced more expensive. Furthermore, under some conditionsof service a harder or even more corrosion resistant surface than thatafforded by zinc is desirable.

The present invention has for one of its chief objects the production ofmalleable cast iron having surfaces more highly resistant to corrosionthan are produced by coating with zinc.

A further object of the invention is the production of malleable castiron with surfaces that are hard and wear resistant as well as beinghighly resistant to corrosion.

Another object of the invention is the provision of an inexpensivemethod of producing malleable cast iron with surfaces of the characterabove referred to.

Other objects of the invention more or less incidental or ancillary tothe foregoing will be apparent from the following description.

In the production of malleable cast iron by the Well known andestablished methods, the

metal is first cast as white iron. In this condition the iron is hardand brittle and can be machined only by grinding. Such castings, with orwithout sand blasting or other definite cleaning operations, are thenpacked in the annealing pots in which they are usually surrounded bygravel or other packing. The gravel tends to reduce oxidation of thecastings during annealing and also serves to support them and preventdistortion at the elevated temperatures. The annealing pots packed withthe castings as described are charged into the annealing furnace and thelatter is then closed and firing started. To properly anneal thecastings a fairly definite heat treatment is required. That is they mustbe raised to and held at an elevated temperature, say 1400 F. to 17 50 Ffor a period of from two to five days. The higher the temperature theshorter the holding period. Then the temperature is allowed to fall, notfaster than 10 F. per hour, until it i has reached about 1000 F. Thedoors of the furnace can then be opened and the pots and their contentsallowed to cool to room temperature. The total time of the commercialannealing cycle may vary, in different plants, from five to fourteendays. As is well known, the resulting castings are strong, ductile andeasily machined as a result of the heat treatment.

My present invention is essentially characterized by the fact that thecoating of the castings is carried out in such a manner that it can'beeffected during the annealing of the white iron castings, with a verygreat resultant saving of time and expense. This result has been madepossible by my discovery of methods of forming alloy coatings withsubstances such as chromium and silicon which involve heat treatmentswithin the temperature range permissible in the annealing of white ironcastings and by procedures which lend themselves readily in otherrespects to lnallcableizing.treatments under commercial conditions. Myimproved methods of forming alloy coatings are not limited to thecoating ofmalleable iron. In fact my copending applications, Serial Nos.242,837 and 242,838, both filed December 27, 1927, have as theirsubjects, respectively, the formation of chromium alloy coatings and theformation of silicon alloy coatings, of general application. Referencemay be had to these latter applications for full detailed disclosures ofthe methods of chromium and silicon coating, and the description in thepresent application will be limited, so fas as the formation of thecoatings is concerned, to such disclosure as is essential to the clearexplanation and illustration of the present invention.

In carrying out my annealing and coating process, white iron castings,preferably after having been thoroughly cleaned, as by sand blasting,are introduced into a suitable chamber (such as an annealing pot)together with 1 material containing a substance (such as chromium orsilicon) adapted to alloy with the iron of the castings and alsocontaining a halogen compound adapted to evolve a nonoxidizing gas orvapor at temperatures below that at which the cast iron oxidizesmaterially say 700 F., and also adapted to react with the said substanceto form a halide thereof which is vaporizable, at least in part, attemperatures below the maximum temperature employed for the annealingtreatment of the castings. The castings and the material contaiued inthe chamber therewith are then subjected to a heat treatment suitable toeffect malleableizing of the castings. That is to say, the container andits contents are placed in a furnace and the temperature is graduallyraised to some suitable temperature ranging from, say, 1400 F. to 17 50F. and there held for a period sufficient to effect the malleableizingof the castings, then slowly cooled to 1000 F, whereupon the furnace isopened and the treating container and its contents allowed to cool toroom temperature.

Upon removing the cooled castings from the annealing pot they are foundto have an alloy coating of the substance, (chromium or silicon, forexample) introduced into the pot. During the annealing heat treatment asthe temperature rises and while still below 700 F., or in other wordsthe approximate minimum oxidizing temperature of iron, the halogencompound present in the annealing pot evolves a halogen or halide gas orvapor which is non-oxidizing and heavier than air, and it displaces anyair present in the pot and prevents oxidation of the castings. Then, asthe heating continues, a temperature is reached, at a point below or inthe annealing range, at which the halogen or halide gas or vapor reactswith the coating substance (chromium, silicon or the like) to form ahalide compound of that substance, which also, at some temperature inthe. annealing range, vaporizes to some extent and diffuses through theannealing pot and contacts with the iron of the castings. In contactwith the iron the last mentioned vaporized compound reacts ordissociates with resulting deposition of the coating substance on thesurface of the casting with the metal of which it alloys to form acoating.

The temperature range of 1400 F.'to 1750 F. above mentioned includes thetemperatures more commonly employed in malleableizing, but there arespecial malleableizing processes that are carried out at othertemperatures, in some cases below and in some cases above the saidrange, and these other temperatures are applicable for coating by myprocess to some, at least, of the coating metals referred to herein.Theoretically there is no definitely fixed lower limit of the range ofmalleableizing temperatures but,

practically speaking, about 1200 F. may be considered the lower limitbecause at temperatures lower than that the increase in the necessarytime of treatment with decrease in temperature is so great as to makesuch lower temperatures impractical. On the other hand, one or morespecial malleableizing processes have been proposed in which thetreatment is carried out at temperatures ranging upward to the point ofincipient fusion of the iron and with a temperature of 1000 C.recommended. However, I believe that approximately 1800 F. marks theupper limit of the range of practically useful malleableizingtemperatures.

As is disclosed in my above mentioned copending applications Serial Nos.242,837 and 242,838, my process of coating with chromium or chromiumalloy can be carried out at temperatures ranging from 1500 F. to 2000 F.and my process of coating with silicon or silicon alloy can be carriedout at temperatures ranging from 1000 F. to 1700 F.

Consequently, considering both the malleableizin and the coating aspectsof my present com ined process and the various coating metals to whichit is applicable, it will be seen that the usefully operativetemperatures of said process cover the entire malleableizing range of1200 F. to 1800 F.

In order that my invention and the method of practicing it may beclearly understood I will now give specific examples pointing out theprocedure in further detail. As has been noted, the methods employed toform the alloy coatings can be carried out under commercial conditionssuitable for annealing of white iron castings and various known forms ofapparatus suitable for such annealing can be employed in carrying outthe present invention. In the interest of clearness I have shown in theaccompanying drawing one or more forms of apparatus that is suitable.

In the drawing, Fig. 1 is a vertical section through a stack ofannealing pots or boxes packed with castings to be annealed and coated.

Fig. 2 is a longitudinal vertical section through an annealing furnacewith annealing pots therein.

Fig. 3 is a transverse section through the same furnace.

C'hromiwm alloy coating.-White iron castings, designated by the numeral1 in Fig. 1 of the drawing, preferably having first been thoroughlycleaned by sand blasting, are placed in a closed bottom annealing pot 2resting on a suitable base 3, together with a packing 4 consisting of 97by weight of ferro-chromium chromium, 0.1% carbon) and 3% bleachingpower (CaOCl), the packing material being crushed to ass a six meshscreen. Additional annea ing weaves pots 5 and 6, similar to pot 2, aresuccessively stacked upon the latter and filled with additional castings1 and packing 4 as indicated. Thus arranged the pot 5 closes the upperend of pot 1 and pot 6 similarly closes the upper end of pot 5, each ofthe pots being preferably provided at its upper edge with an upwardlyextending flange 1 (or 5- or 6, as the case may be). The upper pot 6 isthen closed with a suitable cover late 7 and the joints between the potsand the joint between the cover 7 and the pot 6 are further sealed bylutings 8 of moist clay or the like which serve to largely restrict theescape of gases from the tops of the annealing chamers.

In this manner a suitable number of annealing pots are packed withcastings and these pots or stacks designated as entireties by 9 are thenplaced in a suitable annealing furnace which in the drawing isdesignated as an entirety by the numeral 10, the bases 3 serving tofacilitate handling of the stacks of pots. The furnace at its front endhas the usual charging door 11 and at its rear end is fitted with apowdered coal burner 12 which is arranged to deliver the hot products ofcombustion directly into the furnace chamber as indicated in Fig. 2. Theside walls of the furnace are formed at points near the furnace fioorwith the side ducts 13, 13 which lead to fines 14: which in turncommunicate with a stack or other suitable draft means. The filledannealing pots having been placed in the furnace as stated and thecharging door 11 closed, the firing is started. The entering combustiongases sweep over and around the annealing pots and find exit through theducts 13 and fines 14, as indicated in Figs. 2 and 3 of the drawing.With packing material of the character specified,

the container and packing, they are immediately washed in hot water andthen boiled in a saturated solution of sodium bicarbonate for one-halfhour to remove or neutralize any salts that may remain on the surface of3 the castings. The castings are then washed in water and dried. Thecastings are thus cleansed to remove any halide salts that might adhereto them.

The castings thus treated are found to have, in addition to the usualqualities of high grade malleable castings, a coating of chromium orchromium alloy bright in color and of substantial thickness. The coatinghas an extreme outer layer fairly high in chromium and below this analloy zone hi her in iron. In a specific case of castings subjected tothe last described treatment the compositon of the castings wasapproximately: carbon 2.70%, silicon 0.80%, manganese 0.32%, sulphur0.06%, phosphorus 0.15%, and the coating formed on the castings wasabout 0.001 thick, and the inner alloy layer of the coating containedalittle combined carbon. In this connection, it will be understood thatmy invention is not limited to alloy coatings of any particularcomposition.

Castings with such chromium alloy coatings, in addition to the strength,durability and toughness of ordinary malleable castings have a bright orlustrous appearance that is very pleasing and have the marked advantageof great resistance to oxidation and dilute acid corrosion. Thus suchcastings withstand exposure to the weather and to such acid conditionsas contact with mine water to a remarkable extent not equaled by othercoatings which have heretofore been used for malleable castings. Inaddition the chromium alloy coating gives the casting a hard surfacewell adapting it for various mechanical uses such as clamps and thelike.

While the foregoing detailed procedure is such as I consider suitablefor the production of chromium coated malleable castings, the procedurecan be varied widely within the scope of my invention. Thus the materialsupplying the chromium may be either higher or lower in chromium thanthe material specified above. For example, ferro-chromium containingchromium or even less than 60% may be used. However, with the lowerchromium content very thin coatings result. Again, carbon, silicon,aluminum or other alloying elements may be present in the chromium, andwhile they may 'slow down the coating process, a coating willnevertheless be formed. This fact makes it possible to utilize highcarbon ferro chromium, say 5% carbon, as the source of chromium, withthe decided advantage that it is much lower in price and easier to crushthan is the low carbon ferro-chromium. Also, the packing may be dilutedwith sand, alumina, magnesia, chrome ore or'other refractory materialbut the coating rate is of course decreased by such dilutions. Then,particularly with carbon present, there may be some reduction of suchdiluents which causes the packing to cake and makes the removal of thetreated articles somewhat ditficult.

The temperatures employed in the heat treatment are variable with thecomposition of the packing material and the length of the treatment.Thus, if ferro-chromium less than in chromium or containing carbon,

or otherwise slower acting than the ferrochromium as specified in theabove example, is used, only relatively high temperature anneals (about17 00 F.) will give a good coating. Even with the 70% chromium lowcarbon ferro-chromium, good results are difficult to attain withannealing temperatures much below 1600 F. However, by using commercialchromium (98.1% pure) I have roduced chromium or chromium alloy coatmgsby treating at temperatures as low as 1500 F. In this latter case thechromium metal used was powdered to pass a 100 mesh screen and mixedwith silica sand and anhydrous ferric chloride fine enough to pass a 30mesh screen, in the following proportions Per cent Chromium metal 25Silica sand 74 Ferric chloride 1 The castings, surrounded with thispacking material in a well closed container, were heated to 1500 F. in24 hours and held at that temperature for another 25 hours. With respectto the length of the heat treatment, the time required for the annealingtreatmen itself is sufficient to produce a good coating, with otherhereinmentioned conditions suitable. Exposure to the heat treatment foreven longer periods than usual in the annealing operation do not affectthe coating much, since when once formed the coating increases inthickness but slowly at the temperatures employed. In fact, an annealingtemperature of 17 00 F. for twentyfour hours or more is needed if thepacking material consists of high carbon ferro-chromium (70% chromium,5% carbon) crushed to pass a six mesh screen.

Halogen compounds other than bleaching powder can be used. Thus an equalamount of ferric chloride (preferably anhydrous) can be substituted forthe bleaching powder, though it is to be observed that it tends to makethe packing cake around the castings so that the latter are not soeasily freed. Still other halogen compounds can be employed as has beenpointed out in my copending application Serial No. 242,837, abovereferred to.

As illustrating the use of ferric chloride and at the same time asatisfactory manner of using a diluent in the packing, I have producedmalleable castings with good chromium alloy coatings by using a packingconsisting of about 87% sand blast sand (about six mesh size), 10% highcarbon ferro-chro mium chromium, 5% carbon) crushed to pass a hundredmesh screen, and 3% ferric chloride (anhydrous). The sand, powderedferro-chromium and the chloride are thoroughly mixed together, the lastnamed material causing the powdered metal to adhere to the grains ofsand. In this way the powalso be mixed together with the packingmaterials, which tends to smear the castings with the powdered metal andthe ferric chloride. Using this packing material in the malleableizingprocess with a treating temperature of 1650 F. to 1700 F. for 48 hours,I have secured good coatings on the malleableized castings, particularlyon malleable iron containing about 2.6% carbon. With this packingmaterial the cost of the ferrochromium is reduced and the caking of thepacking material, which tends to occur more or less when ferric chlorideis employed, is minimized.

Silicon alloy coating.-When the castings annealed are to be coated withsilicon or a silicon alloy, the procedure is much the same as in thecase of the coating with chromium. However, in addition to substitutingsuitable silicon material for the chromium material, account must betaken of the fact that the silicon coating is formed more readily thanthe chromium coating. For instance, an over heavy and fragile coating ofsilicon would be formed under the same time and temperature conditionsas would produce a good coating of chromium. For this reason either alower annealing temperature should be used, with a correspondinglylonger period of treatment, or the silicon content can be diluted andthus yield a coating of the desired character. To make the matterspecific, the procedure specified above for the chromium coating can befollowed throughout for the silicon coating if a packing is usedconsisting of 92% silica sand, 5% of ferrosilicon (50% silicon) and 3%of ferric chloride (preferably anhydrous). In coating with silicon Ifind that ferric chloride is preferable to bleaching powder. Also, Ifind that the annealing process is hastened somewhat when coating withsilicon as some of the silicon is taken up by the iron and siliconincreases the rate of graphitization. This addition of silicon tends toaffect even the interior metal of the castings in the manner stated.

The castings that have been silicon coated by my process are bright inappearance and they also have increased resistance to weather andoxidation. However, as to these latter qualities, they are inferior tothe chromium coated castings. The resistance of the silicon coatings toweather, oxidation and acid can be increased by making the coatingsricher in silicon, but this is accomplished at the expense of decreasedt0ughness and mechanical strength of the coatings.

Accordingly, the chromium coating is usually to be preferred.

It is to be observed that while in the case of the chromium alloycoating the process operates most satisfactorily in the upper part ofthe temperature range of 1400 F. to 1750 F. most suitable for annealing,viz. in the part from 1600 F. to 1750 F., in the case of the siliconalloy coating it is preferable to avoid temperatures above about 1700F., the remainder of the annealing range referred to, i. e. 1400 F. to1700 F., being equally applicable to the silicon coating, however. Itwill be understood that the composition of the ferro-silicon employed orthe amount of diluent used in compounding the packing material willdepend upon the range of temperatures of the heat treatment and alsoupon the duration of the treatment, the more dilute silicon materialbeing employed for the higher temperatures and the longer treatments.

The packing material, comprising the active coating materials and. anyinert material employed, can be used over and over again, if activecoating materials are added in sufficient amounts to make up for thedepletion. Indeed, I have found in practice that the process works moresatisfactorily after the packing material has been used one or moretimes in this manner.

As my process is carried out under conditions generally considered to bemost favorable for the proper annealing of the castings, the productsecured has physical characteristics'equaling the normal standard ofgood malleable castings and, in addition, has the above advantages ofthe coating of chromium or other substance.

I am unable to say with certainty precisely what goes on in the carryingout of my process of combined annealing and coating, but as at presentadvised I believe that in addi-' tion to the annealing afi'ect upon thecasting, the following actions occur. In the first stages of theheating, that is, while the temperature is rising to, say, 700 F. andbefore there has been any substantial oxidation of the casting due tothe increase of temperature, the halogen compound constituting one ofthe constituents of the packing material either vaporizes or dissociateswith evolution of chlorine (or other halogen). In either case the vaporor halogen gas formed displaces any air present -in the treatingcontainer and thus obviateso'r at least minimizes oxidation of thecasting, and of the coating material. In case chlorine or other halogenis evolved, even if some slight oxidation of the casting and of thecoating material should occur, the fluxing or etching action of thechlorine cleanses the surface of the resulting oxide scale.' As theheating con tinues with resultant rise of temperature, the

halogen compound in the vapor state, or the chlorine or other halogenevolved, reacts with the coating material (chromium, silicon or thelike) to form a halide thereof. Thus, in the coating with silicon by theuse of ferric chloride, the ferric chloride when heated evolves chlorineby dissociation as follows:

areal. =2FeCl 01 The chlorine thus liberated may react with the siliconthus: I

This reaction is reversible and in the presence of the article to becoated, the silicon chloride would dissociate to form silicon andchlorine. The silicon would immediately alloy with the iron of thecasting being treated at the temperature of the treatment and thehalogen compound would continue to dissociate. The chlorine freed by thedissociation of the silicon chloride would then react with more siliconat points more remote from the iron article and the deposition ofsilicon would thus continue.

Possibly some of the chlorine evolved may rlelact with the iron of thearticle being coated t us:

C1 Fe FeCl This ferrous chloride would have some tendency to dissociateand thus reverse the last reaction, making available part of itschlorineto continue the coating process by forming silicon chloride;Thus, in any case, the chlorine acts as a carrier of silicon, permittingthis element to pass through the vapor state at a lower temperature thanwould otherwise be possible.

As has. been indicated, the halogen compound employed will, when thepacking material is heated, either vaporize and thus displace any airpresent so as to maintain a nonoxidizing atmosphere, or the compoundwill dissociate with the evolution of halogen gas, the action that,occurs being dependent upon the particular halogen compound employed,there being one group of these compounds which vaporizes as stated whenheated and another group which dissociates with evolution of halogengas. Among those in the former group are aluminum chloride, antimonychloride, arsenic chloride, mercuric chloride, phosphorous trichloride,carbon tetrachloride, sulphur monochloride, and'bismuth chloride.Examples of the other class of halogen compounds are ferric chloride,bleaching powder, gold (auric) chloride, cupric chloride, sulphurdichloride, sulphur tetrachloride and phosphorous pentachlochloride. Forthe purpose of my invention I prefer to use members of the latter classof compounds since the halogen gas evolved not only displaces any airpresent and maintains A casting being coated. While I prefer to employone of the chlorides mentioned, especially ferric chloride and bleachingpowder, halogen compounds other than chlorides also can be used. Thus inthe examples given there may be substituted for the bleaching powder orferric chloride a similar amount of anhydrous ferric bromide. However,the cost of the chlorides is lower and their use is preferred.Furthermore, the halogen compound need not be introduced into theheatlng container as such. Thus where ferric chloride is desired amixture of equal amounts by weight of powdered ferrous sulphate(preferably anhydrous) and powdered sodium chloride may be substitutedfor the ferric chloride. On heating the packing these two compoundsreact to give ferric chloride and sodium sulphate. Other known methodsof forming ferric chloride, by reaction within the packing, might beused. However, I prefer to introduce the ferric chloride directly.

It is not necessary that the mixture constituting the packing materialhave the coating material distributed uniformly through it. Thus thecastings to be coated may be dipped in a liquid in which is a heavysuspension of the material that is to form the coating. The sludge thusformed on the casting contains enough of the coating ele ment to give analloy deposit thereof on the casting when subjected to the annealingtreatment in the presence of the halide gas, which latter may beintroduced into the container by placing one of the suitable halogencompounds therein, as will be readily understood.

It should be pointed out in connection with the operation of coatingwith chromium that chromium chloride has a low vapor pressure at thetemperatures suitable for malleableizing and consequently in carryingout my malleableizing and chromium coating process the chromium presentin the treating chamber should be in correspondingly close proximity tothe casting to insure contact of the chromium chloride vapor with thecasting. In some instances it may be found feasible and preferable tosupport the chr0- mium-containing material in such suitably closeproximity to the casting without the use of inert packing material orwithout resorting to the use of a sludge coating on the casting.

It will be understood that the annealing pot and furnace equipment usedmay vary widely. Indeed practically any form of pots and furnacesuitable for the annealing of castings can be employed, provided thatthe pots used have substantially gas tight bottom portions or bottomportions susceptible of being made gas tight. This is important since itis characteristic. of my process that the halogen gas evolved during theprocess, being heavier than air, dis laces air at first present in theannealing c ambers u ward and out through the incomplete y sealed jointsat the tops of said chambers and then maintains the desired atmospherein the chambers through the remainder of the treatment. If the chambersdid not have their bottom parts tightly closed the halogen gases wouldflow out and the effectiveness of the treatment be seriously reduced.

While chromium and silicon, particularly the former, are preferred ascoating materials in carrying out my process, it is to be understoodthat the process in its broader aspects is not limited to thesematerials. Thus the process can be carried out with a suitable amount ofzinc, or aluminum, or antimony, or tantalum (or ferro-tantalum)substituted for the ferro-chromium or ferro-silicon, the zinc, or othermetal, being used preferably in a powdered or finely divided state. Forexample, a coating of zinc or zinc iron alloy can be formed by myprocess by proceeding as in the case of the chromium coating abovedescribed if a packing is used consisting of equal parts, by volume, ofsand and zinc dust. A heavy zinc-iron coating or surface layer is formedon the castings. In coating with zinc the process is operable at varioustemperatures ranging from temperatures well below 1200 F., the lowerlimit of the useful malleableizing range, to 1700 F. Similarly, acoating of tantalum is formed by my process as described for chromium byusing a packing of equal parts, by volume, of sand and ferro-tantalum(80% tantalum) crushed to 20 mesh and finer. In the case of antimony, Ihave produced a bright coating of antimony using a packing having only8% by volume of powdered antimony (through 150 mesh screen) and thebalance sand. The process is operable for coating with antimony orantimony alloy at temperatures ranging from 1500 F. to 1700 F. However,in all these cases the coating of zinc, or tantalum, or antimony hascorrosion resisting qualities distinctly inferior to the coatings ofchromium and of silicon. Malleable castings with coatings of aluminumalso can be produced by my present process, using treating temperatureswithin the range of '1500 F. to 1700 F.

In characterizing herein the gas or vapor evolved in the annealing potsas non-oxidiz- 'ing, that term is of course used in its strict processesof annealing alone and involves little outlay for the materials requiredto form the coating. Furthermore, by reason of the fact thatnon-oxidizing atmospheres are secured and maintained in accordance withmy process by the greatest ease under the normal working conditionsunder which castings are annealed commercially, the process lends itselfespecially well to commercial working.

While I have .set forth specific materials and procedures suitable forthe carrying out of my process, it is to be understood that I have donethis for purposes of explanation and illustration and that the scope ofthe invention is indicated by the appended claims.

lVhat I claim is:

1. The process of forming coated malleable ilon castings which includesthe steps of enclosing a white iron cast-ing in a chamber with materialincluding a metal of the group consisting of chromium, silicon, zinc,aluminum and antimony and a halogen compound adapted, when said materialand casting are heated, to evolve, before the casting becomessubstantially oxidized, a non-oxidizing and etching gas or vapor heavierthan air and capable of reacting with said metal to form a halidethereof vaporizable at least in part at temperatures below the maximumtreating temperature of the process, heating the material and castingand meanwhile permitting the escape from the chamber of the airdisplaced upward by the heavier vapor formed; and continuing the heatingat temperatures between 1200 F. and 1800 F. for a time adapted tomalleableize the casting and simultaneously to form thereon an alloycoating of the said metal.

2. The process of forming coated malleable iron castings which includesthe stepsof enclosing a white iron casting in a chamber with materialincluding a metal of the group consisting of chromium, silicon, zinc,aluminum and antimony and a halogen compound adapted, when said materialand casting are heated to evolve, before the casting becomessubstantially oxidized, a non-oxidizing gas or vapor heavier than airand to react with said metal to form a halide thereof vaporizable atleast in part at temperatures below the maximum operating temperature ofthe process; heating the material and casting and meanwhile permittingthe escape from the chamber of the air displaced upward by thenonoxidizing vapor formed; and continuing the heating at temperaturesbetween 1500 F. and 1700 F. for a time adapted to malleableize thecasting and simultaneously to form thereon an alloy coating of the saidmetal.

3. The process of forming coated malleable iron castings which includesthe steps of enclosing a white iron casting in a chamber with materialcontaining chromium and a halogen compound adapted, when said materialand casting are heated, to evolve, before the casting becomessubstantially oxidized, a nonoxidizing gas or vapor and to react withthe chromium to form a halide thereof vaporizable at least in part attemperatures below the maximum treating temperature of the process; andsubjecting the material and casting to a heat treatment attemperatures'between 1500 F. and 1800 F. for a time adapted tomalleableize the casting and simultaneously to form on the casting analloy coating chromium.

4. The process of forming coated malleable iron castings which includesthe steps of enclosing a white iron casting in a chamber with materialincluding chromium and a halogen compound adapted, when said materialand casting are heated, to evolve, before the casting becomessubstantially oxidized, a nonoxidizing and etching gas or vapor heavierthan air and capable of reacting with the chromium to form a halidethereof vaporizable at least in part at temperatures below the maximumtreating temperature of the process; heating the material and castingand meanwhile permitting the escape from the chamber of the airdisplaced upward by the heavier vapor formed; and continuing the heatingat temperatures between 1600 F. and 1750 F. for a time adapted tomalleableize the casting and simultaneously to form thereon an alloycoating of chromium.

5. The process of forming coated malleable iron castings which includesthe steps of enclosing a white iron casting in a chamber with materialcontaining silicon and a halogen compound adapt-ed, when the materialand casting are heated, to evolve, before the casting becomessubstantially oxidized, a non-oxidizing gas or vapor heavier than airand to react with the silicon to form a halide thereof vaporizable atleast in part at temperatures below the maximum treating temperature ofthe process; heating the material and casting and meanwhile permittingthe escape from the chamber of the air displaced upward by thenon-oxidizing vapor formed; and continuing the heating at temperaturesbetween 1200 F. and 17 00 F. and for a time adapted to malleableize thecasting and simultaneously to form thereon an alloy coating of silicon.

i 6. The process of forming coated malleable iron castings whichincludes the steps of enclosing a white iron casting in a chamber withmaterial containing zinc and a halogen compound adapted, when thematerial and casting are heated, to evolve, before the casting becomessubstantially oxidized, a nonoxidizing gas or vapor heavier than air andto react with the zinc to form a. halide thereof vaporizable at least inpart at temperatures below the maximum treating temperature of theprocess; heating the material and casting and meanwhile permitting theescape from the chamber of the air displaced upward by the non-oxidizingvapor formed; and continuin the heating at tem eratures hetween 1200 and1700 F. and or a time adapted to malleableize the casting andsimultaneously to form thereon an alloy coating of zinc.

In testimony whereof, I hereunto afiix my signature.

LESLIE H. MARSHALL.

